Influence of the Surface Chemistry and Dynamics on an Elasticity-Dependent Macroscopic Supramolecular Assembly

Macroscopic supramolecular assembly (MSA) investigates multivalent supramolecular interactions between large surfaces (exceeding a size of 10 mu m) modified with numerous interactive motifs. Because MSA is the first step to initiate noncovalent interactions at the interface, study of MSA mechanism is significant for various interfacial phenomena such as underwater adhesion, cell-material interaction, self-healing etc. Until now, most researches about MSA mainly report some assembly phenomena by applying molecular interactions into macroscopic assembly, insight into the underlying assembly mechanism is still lacking, e.g. fundamental questions such as what kind of building blocks or surface chemistry is requisite to realize MSA remains to be answered. Especially, multiple variables including surface chemistry, substrate effects, interaction dynamics etc. are significant factors to influence MSA behaviors. Previously we have revealed a rule that the MSA probability declines with increasing substrate rigidity (elastic modulus) under similar surface chemistry and a critical modulus of 2.5 MPa is a boundary condition, above which no assembly occurs. To elucidate the versatility of this rule and investigate the influences of surface chemistry (e.g., interaction type or number) or assembly dynamics on MSA, in this work, we have changed the supramolecular interaction type from beta-cyclodextrin (CD)/azobenzene (Azo) to CD/adamantane (Ad) and increased the interaction number of both CD/Azo and CD/Ad. The results have demonstrated that regardless of varied surface chemistry or interaction dynamics, the MSA probability still displays a negative correlation with the substrate modulus while the boundary modulus is dependent on the strength of the applied supramolecular interaction. For the weak CD/Azo system, 2.5 MPa is a critical value while for the stronger CD/Ad system this boundary value increases to 3.3 MPa. We envision that these fundamental understandings of the MSA mechanism may favor for establishing a general design principle of MSA systems and interpreting interfacial phenomena.